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J^ 9089 



Bureau of Mines Information Circular/1986 



Impact of Background Sources on Dust 
Exposure of Bag Machine Operator 

By Andrew B. Cecala and Edward D. Thimons 




UNITED STATES DEPARTMENT OF THE INTERIOR 



^au^''>^ ' ^^" ^ 



. / 



Information Circular 9089 



Impact of Background Sources on Dust 
Exposure of Bag Machine Operator 

By Andrew B. Cecala and Edward D. Thimons 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Model, Secretary 

BUREAU OF MINES 
Robert C. Morton, Director 






f)0 



Library of Congress Cataloging in Publication Data: 




Cecala, Andrew B 

Impact of background sources on dust exposure of bag machine 
operator. 

(Information circular/Bureau of Mines; 9089) 
Supt. of Docs, no.: I 28.27:9089. 



1. Mineral industries -Hygienic aspects. 2. Bagging -Hygienic aspects. 3. Mineral 
dusts -Measurement. I. Thimons, Edward D. H. Title. HI. Title: Dust exposure of bag 
machine operator. IV. Series: Information circular (United States. Bureau of Mines); 9089. 



TN295.U4 



[TH7697.M56] 



622 s [622'.8] 



86-600121 



CONTENTS 



7. Case 6 

8. Case 7 

9. Case 8 
10. Case 9 



TABLE 
1. Nine cases of background dust exposure to bag operator, 



Page 



Abstract 1 

Introduction 2 

Testing setup 2 

Results 3 

Discussion 7 

Conclusion 9 

Appendix. — Calculations to determine TLV exposure time..... 10 

ILLUSTRATIONS 

1. Sampling setup to monitor a worker's dust exposure 3 

2. Case 1: Operator's exposure after becoming soiled with product from fill 

nozzle that did not shut off 4 

3. Case 2: Operator's exposure after becoming soiled with product while 

changing the saddle height 4 

4. Bag operator after becoming soiled with product 5 

5. Case 3: Operator's exposure from blowing clothes with compressed air 6 

6. Operator's exposure from broken bag at fill station. Case 4 (>1 ) and 

case 5 (^) 6 



Operator's exposure from broken bag during conveying process 6 

Operator's exposure from bulk loading outside 7 

Operator's exposure from bag hopper overflowing 7 

Operator's exposure from coworker sweeping floor one level down.. 7 





UNIT OF MEASURE 


ABBREVIATIONS 


USED IN THIS REPORT 


h 


hour 


mm 


millimeter 


h/d 


hour per day 


mg/m3 


milligram per cubic meter 


lb 


pound 


min 


minute 


ym 


micrometer 


pet 


percent 



IMPACT OF BACKGROUND SOURCES ON DUST 
EXPOSURE OF BAG MACHINE OPERATOR 



By Andrew B. Cecala^ and Edward D. Thimons^ 



ABSTRACT 

The Bureau of Mines has recorded a number of different background dust 
sources that significantly contaminated the air breathed by bag machine 
operators. These background sources, observed at five different plants 
over the past 2 years, can expose bag machine operators to more signifi- 
cant dust concentrations than the filling process itself. To keep bag 
operator exposure within acceptable dust levels established by the Mine 
Safety and Health Administration, U.S. Department of Labor, the signifi- 
cance of these background sources must be realized, and the sources must 
be identified and controlled. The purpose of this work is to identify 
common background dust sources and show the significant effects that 
they have on the bag operator's overall dust exposure. 



Mining engineer, 



^Supervisory physical scientist. 
Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 



INTRODUCTION 



The purpose of this report is to iden- 
tify some common background dust sources 
in and around the bag-filling area. Al- 
though these background dust sources are 
often unrecognized, they can be more sig- 
nificant sources of contamination than 
the dust generated from the bagging 
process. 

The bagging of mineral products into 
50- and 100-lb paper bags is common 
throughout the entire mineral processing 
industry. Bagging is performed by a bag 
operator who sits in front of a two- or 
four-station fill machine. The bagger's 
function is to attach empty bags to the 
fill nozzles as filled bags are ejected 
from the machine. If the product being 
bagged is extremely fine (smaller than 
200 mesh), the bag operator's dust expo- 
sure is usually one of the highest in the 
plant. 

The bag operator is exposed to two pri- 
mary dust sources. The first is product 
blowbaok during the bag-filling cycle. 
This occurs as excess pressure is re- 
leased from around the fill nozzle during 
filling. As the excess air forces its 
way out of the bag, product is forced out 
with it. This blowback of product leav- 
ing the bag creates a considerable amount 
of dust. The second major source is the 
"rooster tail" of product thrown from the 
bag valve and fill nozzle as the bag is 
ejected from the fill machine. Since the 
bag is pressurized as it leaves the ma- 
chine, product spews out of the valve for 
a few seconds. 



These two known dust sources must be 
controlled to reduce the exposure of the 
bag operator. However, even when this is 
done, the operator's exposure often re- 
mains over the threshold limit value 
(TLV) established by the Mine Safety and 
Health Administration (MSHA) . This is 
due to background dust sources that, 
in most cases, are not recognized by 
plant personnel. Gravimetric dust mea- 
surements, which are the standard dust 
measurements taken at most plants, only 
indicate the overall dust exposure of 
the worker averaged over an 8-h day. 
They do not identify the different 
sources or the magnitude of the exposure 
for specific periods during the workday. 
Since respirable dust is not visible to 
the unaided eye, many background dust 
sources are difficult to identify. To 
get an indication of the significance of 
each source, an instantaneous dust moni- 
tor must be used. Then, as different 
background-dust-producing events take 
place during the workday, increased dust 
concentrations and their related effects 
can be determined. 

This report presents common plant oc- 
currences that increase the bag opera- 
tor's dust exposure over the standard 
baseline for dust generated at the fill 
station (blowback and rooster tail). 
These background sources were observed at 
five different plants. 



TESTING SETUP 



Bag operators were monitored to deter- 
mine their dust exposure at the work sta- 
tion. The dust monitor used in all cases 
was a real-time aerosol monitor (RAM-1) 
developed by GCA Corp. under a Bureau of 
Mines contract. This instrument uses a 
light-scattering device to determine the 
dust concentration of a sample drawn in 
from the environment through a 10-mm cy- 
clone. It is sensitive to changes in the 
dust content (size, shape, refractive 
index) , but if calibrated to a specific 
dust, its accuracy is within plus or 



minus 10 pet of gravimetric samplers sim- 
ilarly equipped with the standard 10-mm 
cyclone. ^ 

The 10-mm cyclone was used to sample 
the respirable fraction of dust. This 
cyclone is used in the United States for 
dust compliance sampling. The cyclone 
classifies "respirable" size particles 

^Williams, K. L., and R. J. Timko. 
Performance Evaluation of a Real-Time 
Aerosol Monitor. BuMines IC 8968, 1984, 
20 pp. 



that reach the alveolar regions of the 
lungs, and are usually considered to have 
aerodynamic diameters (AED) of 10 ym or 
less. 

The cyclone was attached to the bag op- 
erator's lapel to give an accurate indi- 
cation of his dust exposure. The cyclone 
was connected to the dust monitor 
by tubing to allow the operator to work 
with minimal interference (fig. 1). 

The signal from the RAM-1 dust monitor 
was fed into a strip-chart recorder, a 
continuous trace of the bag operator's 
dust exposure was recorded relative to 



time. The times of different dust- 
producing occurrences throughout the 
plant were noted. When an occurrence ap- 
peared to increase the operator's dust 
exposure, that time segment was analyzed 
using a planimeter to calculate the area 
under the curve for that time period, and 
an average concentration for that period 
was then calculated. The increase in the 
bag operator's exposure due to the back- 
ground source was established by compar- 
ing the operator's baseline dust con- 
centration with the increased exposure 
associated with the background source. 



RESULTS 



The first three cases involve increased 
exposure of bag operators due to their 
clothes becoming contaminated by product , 
which is emitted as they perform their 
work. Figure 2 shows a case in which the 
bag operator became soiled with product 
from a fill nozzle that did not shut off 
after the bag had ejected from the fill 
machine (case 1). The operator's re- 
corded dust concentration before this 
happened was approximately 0.1 mg/m^; 
this increased to 1.01 mg/m^ after becom- 
ing soiled with product. Figure 3 shows 
a similar occurrence when the bag opera- 
tor became contaminated with product when 
accidentally hitting the fill button 
while changing the saddle height (case 
2). Since there was no bag on the noz- 
zle, product flowed from the fill nozzle, 
soiling his clothes and increasing his 
dust exposure level from 0.07 mg/m^ to 
1.15 rag/m^. In both cases, the back- 
ground dust source was the operator's 
work clothes. Figure 4 shows an operator 
soiled with product. In a case such as 
this, clothes should be changed or 
cleaned using a vacuum system. Figure 5 
shows a case where an operator finished 
bagging and cleaned his clothes using 
compressed air (case 3), which is not an 
acceptable cleaning technique. His dust 
exposure increased substantially, from 
0.19 mg/m^ to 0.45 mg/m^ as he dusted 
off. In all three cases, the dust source 
was considered background because it was 
not being generated by the bag-filling 
operation. The operator was contaminated 
originally from the bag-filling process. 



but if the clothes were properly cleaned, 
his dust exposure would be minimized. 




FIGURE 1.— Sampling setup to monitor a worker's dust ex- 
posure. 




18 21 23 

TIME, min 
FIGURE 2.— Case 1: Operator's exposure after becoming soiled with product from fill nozzle that did not shut off. 




16 20 

TIME, min 
FIGURE 3.— Case 2: Operator's exposure after becoming soiled with product while changing saddle height. 



These next three cases deal with in- 
creased dust exposure from broken bags of 
product material, two cases of a broken 
bag at the fill station, and one of a 
broken bag during the conveying process. 
In most cases, bags break because of 
flawed bags delivered from the manufac- 
turer and not due to ripping by the oper- 
ator or the conveyor. Figure 6 (panels A 
and B) shows cases 4 and 5, in which the 
bag operator's exposure was from a broken 
bag at the fill station. In case 4, dust 
exposure was increased from 0.07 mg/m^ 
to 0.40 mg/m^ immediately following the 
bag breaking; in case 5, the operator's 
exposure went from 0.11 mg/m^ to 0.35 
mg/m^ immediately following the break. 



In figure 7, the bag operator's dust ex- 
posure was from a broken bag during the 
conveying process (case 6). Dust expo- 
sure increased from 0.07 mg/m^ before to 
0.48 mg/m^ after the bag broke. In this 
case, even though the bag broke during 
conveying, dust contaminated the air in 
the mill substantially, then flowed into 
the bagging room where the operator is 
located. This occurs because the exhaust 
ventilation system in the bag loading 
area creates a negative pressure that 
draws background air in from the mill. 

The next three cases are all somewhat 
different, except that in each case the 
bag operator was totally unaware of the 
additional activity or background source 




FIGURE 4.— Bag operator after becomlrtg soiled with product. 



2.0 



lO 



E 



5 
q: 



o 

z 
o 
o 

O 




4 6 

TIME, min 



10 



FIGURE 5.— Case 3: Operator's exposure from blowing 
clothes with compressed air. 



that was increasing his dust exposure. 
In case 7, a truck was being bulk loaded 
outside the mill where bagging was being 
performed. The dust generated from this 
bulk-loading process traveled through an 
open door into the mill, contaminating 
the bag operator (fig. 8). The bag oper- 
ator's dust exposure of 0.17 mg/m^ before 
bulk loading began outside and increased 
to 0.42 mg/m^. Over the period of the 
day, there can be a substantial number of 
trucks bulk loaded at this position, 
depending upon customer orders. In the 
second instance, the bag hopper feeding 
the bag machine overflowed with product 
(case 8). As the product fell to the 
floor, a substantial amount of dust was 
dispersed (fig. 9). The operator's expo- 
sure was increased from 0.06 mg/m^ to 
0.73 mg/m^ after the hopper overflowed. 
In the last case, a coworker in the mill 
was sweeping the floor one level below 
with a push broom, and the operator's 
exposure increased from 0.03 mg/m^ to 
0.17 mg/m^ (fig. 10). Sweeping is an 



E 

E 

z" 

o 

^ 

I- 
z 

UJ 

o 
z 
o 
o 

\- 

V) 

o 



2.0 



1.5 - 



1.0 



.5 



3 




9 12 

TIME, min 




5 10 

TIME, min 

FIGURE 6.— Operator's exposure from broken bag at fill sta- 
tion. A, Case 4; B, case 5. 



2.0 




10 
TIME, min 

FIGURE 7.— Case 6: Operator's exposure from broken bag 
during conveying process. 



unacceptable method of cleaning the 
floor because of the dust it generates. 



Washing the floor with water, or vacuum- 
ing are the only two acceptable methods. 



DISCUSSION 



The results showed that a number of 
different background sources can signifi- 
cantly increase the bag operator's dust 
exposure. For bag operator exposure to 
remain within acceptable dust levels as 
established by MSHA, dust from the bag- 
ging process and background dust sources 
must be controlled. 

The TLV for respirable dusts containing 
quartz (silica) is calculated by the fol- 
lowing equation: 



10 



pet silica + 2 



= mg/m3 . 



In practice, personal samplers are at- 
tached to worker's breathing zone for 
a normal 8-h workday. The respirable 




8 12 

TIME, min 

FIGURE 8.— Case 7: Operator's exposure from bulk loading 
outside. 



particles are collected on a filter and 
weighed to determine the average 8-h 
exposure. This quantity is then compared 
with the TLV calculated from the above 
equation. The percent silica is deter- 
mined by testing the material retained 
on the filter, generally by X-ray def Tac- 
tion. A sample having 100 pet silica on 
the filter will establish a TLV for the 
operator of 0.1 mg/va? , Many times at 
silica sand operations, although pure 
ground silica is being bagged, the silica 
content of the respirable dust is in the 
50- to 80-pct range; thus, the TLV for 
these plants is in the 0.20- to 0.12- 
mg/m3 range. With these low TLV dust re- 
quirements, every effort must be made to 
eliminate the background dust sources. 

Table 1 shows the bag operator's expo- 
sure for each case showing the before and 
after dust concentration with reference 
to the background event, and the amount 
of increase over previous concentrations 
(before) , which show as increase factor. 
The TLV exposure time represents the 
length of time necessary for the operator 
to exceed his 8-h TLV standard when ex- 
posed to the background dust source at 
the measured dust level. This is assum- 
ing a 50-pct silica content, which corre- 
sponds to a 0.2 mg/m3 standard. The 
method used to calculate this TLV expo- 
sure time is presented in the appendix. 



1.5 



' ' 1 
Normal |Jk 


1 I 1 ' 1 ' 



.5 - 



8 12 

TIME, min 



20 



FIGURE 9.— Case 8: Operator's exposure from bag hopper 
overflowing. 



to 

E 

E 



O 

o 

H 




TIME, min 

FIGURE 10.— Case 9: Operator's exposure from coworker 
sweeping floor one level down. 



TABLE 1. - Nine cases of background dust exposure to bag operator 





Description 


Dust cone, mg/m3 


Increase 
factor 


TLV exposure 


Case 


Before 


After 


time using 
0.2-mg/m3 std 


1... 
2... 


Malfunctioning fill nozzle 
Start button hit 


0.10 
.07 
.19 
.11 
.07 
.07 
.17 
.06 
.03 


1.01 
1.15 
.45 
.35 
.40 
.48 
.42 
.73 
.17 


10.1 
16.4 
2.4 
3.2 
5.7 
6.9 
2.5 
12.2 
5.7 


1 h 35 min 
1 h 23 min 


3... 


Blowing clothes. .......... 


3 h 33 min 


4... 
5... 
6... 
7... 
8... 
9... 


Broken bag-fill station... 
...do 

Broken bag-conveying 

Bulk loading outside 

Bag hopper overflowing, . , . 
Sweeping floor 


4 h 34 min 
4 h min 
3 h 20 min 
3 h 48 min 
2 h 11 min 
9 h 24 min 



What must be considered with this TLV 
exposure time is the duration of each oc- 
currence. In case 3, when the operator 
is blowing dust from his clothes with 
compressed air, the dust exposure dura- 
tion would be relatively short, since it 
is unrealistic that an operator would 
blow dust from his clothes for 3.5 h/d. 
On the other hand, there are examples 
where one occurrence can overexpose an 
operator (cases 1 and 2) where his 
clothes have become contaminated with 
product. The bag operator's dust expo- 
sure in both cases remain at significant 
concentrations 30 min after becoming con- 
taminated. If the operator decided to 
finish loading the truck, or to wait un- 
til break time to clean his clothes, he 
would be overexposed in 1.5 h, which em- 
phasizes the importance of not wearing 
previously soiled clothes. This would be 
especially relevant in cold weather when 
workers are wearing jackets that may not 
be cleaned for long periods of time. 

Another factor in the TLV exposure time 
is the amount of air that is contaminated 
by the background source. This is most 
obvious with the three cases involving 
broken bags. When the bags broke at the 
fill station (cases 4 and 5) , the product 
fell through a wire mesh conveyor into a 
hopper to recycle the product. The ex- 
posure time ranged between 5 and 15 min. 
When the bag broke on the conveyor, the 
significant exposure time was much longer 
because the breakage contaminated a 
greater volume of air. All the product 
either remained on the belt or fell to 
the floor, generating a substantial 



amount of dust and contaminating a large 
volume of air. Because of this, the ex- 
posure time doubled from that of the bag 
breakage at the fill machine. 

It must be realized that the bag oper- 
ator can be overexposed when a very small 
number of these background sources occur. 
The following are a few common background 
sources observed and an estimate of the 
number of occurrences necessary for the 
operator to be overexposed: 



Soiled clothing 

Bag breakage: 

During loading. . . . . 

During conveying. . . 
Bulk loading outside. 
Bag hopper overflow.. 



Number of 
occurrences 



14-18 
6-10 
3- 4 
3- 4 



It must be remembered that these dust 
sources are site related. A significant 
background source at one plant might be 
insignificant at another. 

It is evident from table 1 that each of 
the background dust sources had signifi- 
cant effect on the bag operator's dust 
exposure and the importance of control- 
ling these sources is clear. In each of 
these cases, the background dust ex- 
posure could be eliminated or reduced. 
An operator who becomes soiled with prod- 
uct should immediately vacuum or change 
his clothes. He should not blow dust off 
them with compressed air (case 3) . If 
broken bags are a problem, the answer 
might be to go to a better bag, for 



example, a bag using stress kraft paper 
or possibly a bag with additional plies. 
A solution for contaminated mill air 
might be to draw the air into the bag 
room from a location away from the 
loading activity, or to filter the 
air using a canopy air curtain device. 4 
Contaminated air from dutside the mill 
should never be permitted to flow into a 
building and to contaminate workers as in 



case 7 where bulk loading was being per- 
formed. Also, sweeping should not be 
performed. 

These case studies are designed to show 
the extent and seriousness of background 
dust sources in terms of the bag opera- 
tor's overall dust exposure. A number of 
dust control techniques are available to 
deal with these background sources. ^ 



CONCLUSION 



The bagging of mineral products into 
paper bags is common throughout the min- 
eral processing industry. The bag opera- 
tor's dust exposure at these plants is 
usually one of the highest recorded for 
the plant, especially when the product 
being bagged is very fine (smaller than 
200 mesh). Frequently, events not di- 
rectly related to the bagging opera- 
tion may be more significant sources of 
contamination than the bagging process 

^U.S. Bureau of Mines. Dust Free Work 
Station for Minerals Processing. Tech- 
nol. News, No. 230, Oct. 1985, 35 pp. 



itself, sometimes increasing the opera- 
tor's exposure 10 times normal. In cases 
where the operator's TLV is low because 
of high silica content, these background 
sources have been shown to overexpose an 
operator in less than 2 h. To effective- 
ly keep bag operator exposure at accept- 
able dust levels, these background dust 
sources must be controlled. 

^National Industrial Sand Association. 
Guidance and Solutions to Reducing Dust 
Levels in the Bagging of Whole Grain Sil- 
ica Product. Silver Spring, MD, 1977, 
35 pp. 



i4t^'V 



IS 



10 



APPENDIX. —CALCULATIONS TO DETERMINE TLV EXPOSURE TIME 



To calculate the workers' TLV exposure 
level, the following equation is used: 



10 



pet silica + 2 



= mg/m^ . 



1. Assume 50 pet respirable silica 
content, which calculates to be a I'LV 
value of 0.192 mg/ra^ . For convenience, 
this value will be rounded off to 0.2 
ing/m^ . 

2. This means that the workers' aver- 
age dust exposure over the 8-h day, must 
not exceed 0.2 mg/m^ , 

8 h X 60 min = 480 min 



480 min x 0.20 mg/nP = 96 mg min/nP . 

3. By knowing the dust concentration 
for a particular occurrence, for example 
the 1.01 mg/nP in case 1, and by dividing 
this 1.01 value into 96, the TLV exposure 
time can be determined. 

96 mg min/n^ -i- 1.01 mg/m^ 

= 95 min, or 1 h 35 min. 

4. This means that at a dust concen- 
tration of 1.01 mg/n^ , in 1 h and 35 min, 
the worker will reach his TLV level. 



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